In order to make a telephone call, you pick up a telephone and release the hook switch (the piece of the phone on the receiver you press to get a dial tone or to hang up, or the ON/OFF button on cordless phones). Marshall explains that act basically tells the phone company you want to make a call. When you hear a dial tone, you dial your number.
The phone company gets the number you're calling and makes a path for it, or routes the call, to its destination. There are buildings across the globe that house telephone switching equipment, as well as fiber optic cables that flow between them. In split seconds, computers patch together a set of cables and figure out precisely how to direct your call. The moment the path is established, the phone rings and you're ready to chat.
As you speak into your telephone's microphone, the sound waves are turned into an electrical signal so that it can flow through the network along copper wires. On the other end of the line, a phone takes the signal and uses the speaker to convert the electrical signal back into sounds waves.